Kevin starts counting at 48, and he counts by threes. If 48 is the 1st number that Kevin counts. what is the 15th number that he counts?
Explanation: What is the first number that he counts? $48$ What is the second number that he counts? $\begin{align*}&48 + 3 \\ &= 51\end{align*}$ What is the third number that he counts? $\begin{align*}&48 + 3 + 3 \\ &= 48 + (2 \times 3) \\ &= 54\end{align*}$ What is the 15th number that he counts? $\begin{align*}&48 + (14\times3) \\ &= 48 + 42 \\ &= 90\end{align*}$